ORTHOGRAPHIC PROJECTIONS
An orthographic projection is a technique used in technical drawing and engineering to represent a three-dimensional object in two dimensions. It provides a series of flat, two-dimensional views of an object from different perspectives. These views, called orthographic views, show the object as if it has been projected onto an imaginary box with planes that are perpendicular to each other.
In an orthographic projection, the object is typically shown in three main views: front view, top view, and side view. The front view represents the object as it would appear when looking directly at its front face. The top view shows the object as if looking down from above, and the side view displays the object from the side.
Each view provides specific information about the object's dimensions, shape, and features. By combining these different views, viewers can understand the object's complete geometry and how its various parts relate to each other in a detailed and precise manner.
Orthographic projections follow specific conventions and use standard symbols and lines to represent various features such as edges, surfaces, and hidden lines. These projections are widely used in fields like engineering, architecture, manufacturing, and design, where accurate and clear representation of objects is crucial for communication and construction purposes.
Background Knowledge:
Multiview Drawings
Another name for an orthographic projection is a multiview drawing. The standard three views of a multiview drawing are front, right side, and top view. These are the views drawn in an orthographic projection because a person looking at the drawing can see all the important aspects of that drawing needing only these views. The best way to think about how to get these views from a 3D object is to imagine the object in a glass box.
Glass Box Theory
Imagine that the object is inside a glass box and we are drawing the surfaces projected onto the glass box. If you were to open the box and unfold it, what you would see projected is the 2D views.
Once the box is unfolded you will have multiple 2D representations of your 3D object. These views are labeled based on the orientation you are looking at the object. Generally speaking the front view is the view that contains the most information on the object and from there you can assign the other views. The right and left side views are to the right and left of the front view. The top and bottom are you guessed it, the top and bottom based off of the front view and the back view is the view behind the front view.
In general though the only three views that are used is the front, top and right side because the other views only repeat the information given in those three. There are times when only two views are required because you can convey all the information with only those two views but in general we will be working with the standard three view drawing when talking about orthographic projections.
Practice Problems - Orthographic Projections
Look at each object's 3D isometric view and try to find which orthographic projection represents the object. There is only one correct answer for each object. Pay careful attention to what would be a hidden line based on the orientation you are looking at the object.
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PRACTICE HAND DRAFTING ORTHOGRAPHIC DRAWINGS
Hand drafting an orthographic projection involves creating a two-dimensional representation of a three-dimensional object using a set of standard drawing techniques. Orthographic projection is a method of representing objects in a way that shows their true shape and size without distortion. Here are some basic steps to hand drafting an orthographic projection:
Gather your materials: You'll need a drawing board, drawing paper (preferably with a grid), a mechanical pencil or drafting pencils of different lead thicknesses (e.g., 0.5mm, 0.7mm), an eraser, and a set of drafting instruments like a T-square, triangles, and a compass.
Understand the object: Study the object you want to draw and visualize how it would appear in different views (front, top, and side). Familiarize yourself with the object's dimensions, shapes, and features.
Decide on the scale: Determine the scale at which you want to draw the orthographic projection. For example, 1:1 represents the actual size, while 1:2 means each dimension will be half the actual size.
Choose the views: Select the views you want to include in your orthographic projection. The most common views are the front, top, and side views, but additional views may be necessary depending on the complexity of the object.
Set up the drawing paper: Place the drawing paper on the drawing board and secure it with clips or tape. Use a T-square to draw a horizontal baseline across the paper, representing the ground or floor line.
Draw the front view: Position your object on the baseline and use the T-square and triangles to draw the front view of the object. Start with the basic outline, focusing on the main features, and then add details such as curves, edges, and dimensions. Use light, construction lines initially and refine them as you progress.
Draw the top view: Using the same technique, draw the top view of the object directly above the front view. Ensure that the lines align properly with the corresponding lines in the front view.
Draw the side view: Again, using the same technique, draw the side view of the object to the right of the front view. Ensure that the lines align properly with the corresponding lines in the front view.
Add dimensions: Add accurate dimensions to the orthographic projection, including lengths, heights, and depths. Use arrows and dimension lines to indicate the measurements.
Finalize the drawing: Once you're satisfied with the accuracy and level of detail, darken the lines of the orthographic projection. Erase any unnecessary construction lines and make sure the drawing is clean and presentable.
Remember, hand drafting an orthographic projection requires practice and attention to detail. Take your time, use the appropriate tools, and refer to drafting standards and conventions to ensure your drawing is clear and precise. Anyone should be able to pick up your drawing and be able to produce what you drew.
Drawing 1: ANVIL
A good drawing to start hand drafting orthographic projections. The only thing you should be aware of is reproducing the angled faces. When looking at them from the top and side view you will see them as straight object lines. Which is why you draw more than one view since some information is lost if you do not show all pertiniant sides of an object.
Step 1
Find the center of your paper to see where you should place your views
Step 2
Draw the front view with the side of the view in line with the center mark and at least an inch from the title block to leave room for dimensions
Step 3
Draw the construction lines that you will need to transfer the important features from the front view to the other views. Notice I have included the 45 degree angled transfer line to transfer things from the top view to the side.
Step 4
Draw in the object lines for the top and side view. Make sure the spacing is equal with the front view and that they line up with each other. The space will be used for dimensioning the drawing.
Step 5
Step 6
Clean up the drawing and add dimensions.
Drawing 2: SLIDE
The angle on the front face is not given but there is enough information given to be able to draw all the views. You will need the angled transfer line to transfer the location of the angled face from the side view to the top view.
Drawing 3: LOCK FINGER
First drawing with circles and arcs. Remeber a circle from the side is just a rectangle. Be sure to follow demsioning rules and only give a diameter or radius dimension from the face where it is visible and not to the hidden lines.
Drawing 4: BEARING
The front view is missing but there is enough information given to be able to produce the front view for your drawing. Other than that a straight forwards drawing.
In case you were wondering, the answers to the practice problems are : BEH, FJK, ILD, CGA